We propose to isolate, purify, and characterize specific human genes. We plan to develop the technical means of isolating a human gene which has a base sequence complementary to human ribosomal RNA. This is for the prupose of learning the chemical and physical properties of a unique human genetic sequence. For isolation, the successive steps are: 1) purification of 100 mgm of human DNA from human spleens, 2) enrichment for DNA by partial melting and nitrocellulose chromatography, 3) CsCl equilibrium centrifugation and separation of DNA with the specific gravity of 1.72 gm/ml, and 4) further purification by Ag ion complexing and CsSO4 equilibrium centrifugation. In addition, the human gene will be studied by isolating RNA/DNA hybrids after hybridization in solution and successive CsCl equilibrium centrifugations. The degree of purification for each step of all isolations will be assayed by the nitrocellulose disc assay of Gillespie and Spiegelman. The degree of effectiveness of each step will be assayed by rRNA/DNA hybridization with H3-uridine RNA prepared from an auxotroph uridine. The purified genes will be characterized by their physical characteristics such as specific gravity, MW, melting, and kinetics of reannealing. This will permit us to assess the spacer regions and the inter-loci heterogeneity.